This invention relates to a steel material for a colored spring, a method for producing a colored spring, and a colored spring.
Springs such as helical springs and plate springs are indispensable parts in assembling a variety of machines. Steel materials for spring are divided roughly into steel wires and steel plates. The steel wires are classified further into hard steel wires, piano wires and stainless steel wires specified in JIS or Japanese Industrial Standard. These basic steels have very similar surface color tone. Particularly, the hard steel wires and the piano wires are indistinguishable only based on the surface color tone.
The stainless steel wires have generally excellent gloss compared to the hard steel wires or the piano wires, and therefore it is not difficult to distinguish the hard steel wires or the piano wires from the stainless steel wires. However, the case that a so-called oil drawing or wet drawing, in which the wire is drawn by applying a tensile force while applying oil to the surface of the wire, is performed to the hard steel wires or the piano wires, these wires exhibit increased gloss. As a result, the hard steel wires or the piano wires become indistinguishable from the stainless steel wires.
The fact that the type of spring is indistinguishable based on the surface color tone as described above will cause the problem that springs which are different in type but similar in shape would be used inadvertently together in the manufacturing process of various machines. Accordingly, the springs are colored to avoid this problem.
FIGS. 5A and 5B show conventional coloring methods in producing springs. As shown in these figures, the conventional methods for coloring spring can be classified roughly into the method A shown in FIG. 5A according to which the coloring is applied before springs are formed and the method B shown in FIG. 5B according to which the coloring is applied after springs are formed.
More specifically, according to the conventional method A, the basic steel is first colored. Subsequently, a wire drawing is applied in the case that the basic steel is a steel wire, whereas a rolling is applied in the case that the basic steel is a steel sheet. The basic steel which has been colored and drawn/rolled are then shaped into springs using a specified shaping apparatus. Thereby, intermediate products can be obtained. These intermediate products are made into springs through a process of annealing the intermediate products loaded in an annealing furnace at a specified temperature. According to this method, the basic steel is already colored before being formed.
According to the conventional method B, the basic steel is plated or lubricated, but is not yet colored, before being formed. Then, similar to the conventional method A, after a drawing or rolling is performed, a specified shaping operation is performed in a shaping process. In this way, intermediate products in the form of springs can be obtained. These intermediate products are annealed and then colored. As a coloring method, either a chemical conversion treatment or color plating treatment is performed.
In the conventional method A, there can be specifically used, as a coloring method, a resin coating method of coating the surface of the basic steel with special resin, a baking finish method of baking paint on the surface thereof. In the conventional method B, a chemical conversion treatment for treating the basic steel with chemicals and an electroplating treatment can be used as a coloring method.
Incidentally, as a color tone of the final spring, black is in many cases particularly preferably adopted in order to coincide the surface color tone with the black base color tone or to meet a demand in design. Both the electroplating treatment and the chemical conversion treatment are applicable to make springs black. Specifically, a black chromium plating treatment, a black nickel plating treatment, a black rhodium plating treatment and the like are used as an electroplating treatment. A black chromate method and a black oxide finish method are used as a chemical conversion treatment.
However, the steel material for springs is subjected to an exceedingly large abrasion from a variety of shaping machine tools during the shaping process. Accordingly, coatings and paints are often scratched or peeled by the large abrasion, if the basic steel is colored according to the conventional method A in which the coloring is performed by coating with resin or painting before the shaping process.
Normally, the springs are heated at a temperature of 250.degree. to 400.degree. C. for 2 to 30 minutes in order to improve the spring characteristic (a low temperature annealing treatment). Thus, even if scratches made by the abrasion is of a slight degree, the coats or paints fuse during this heating treatment, causing the springs to stick to each other. As a result, recesses are undesirably formed on the outer circumferential surfaces of the springs through the softening and fusing of the coats.
Further, there is sometimes employed a shaping apparatus provided with a detector for detecting the size of a spring using an electric signal during the shaping process. In order to employ such a shaping apparatus, the surface of the steel material must be in a conductive state. When the surface of the steel material is covered with a coating or paint layer, it is brought into an insulated state. Thus, the shaping apparatus provided with the detector cannot be used.
For the aforementioned reasons, it has been problematic to color the surface of the basic steel using the conventional method A. On the other hand, the conventional method B has the problem of increasing the production costs since a cumbersome treatment, e.g., a chemical conversion treatment or color plating treatment, must be performed to color the intermediate products that have passed through the annealing process.